Temperature compensation for an analyte measurement determined from a specified sampling time derived from a sensed physical characteristic of the sample containing the analyte

ABSTRACT

Various embodiments for a method, systems and meters that allow for a more accurate analyte concentration with a biosensor by determining at least one physical characteristic of the sample and compensating for the effects of ambient temperature with a defined relationship between temperature in the environment, the meter or the biosensor.

CROSS-REFERENCE

This DIVISIONAL application claims the benefits of priority under 35 USC§§ 120 and 121 from prior filed U.S. application Ser. No. 13/929,495filed on Jun. 27, 2013, allowed, which prior filed application (Ser. No.13/929,495) claims the benefits under 35 USC §§ 119 and 120 of priorfiled U.S. Provisional Application Ser. No. 61/840,176 filed on Jun. 27,2013, which applications are incorporated by reference in their entiretyinto this application.

BACKGROUND

Electrochemical glucose test strips, such as those used in the OneTouch®Ultra® whole blood testing kit, which is available from LifeScan, Inc.,are designed to measure the concentration of glucose in a physiologicalfluid sample from patients with diabetes. The measurement of glucose canbe based on the selective oxidation of glucose by the enzyme glucoseoxidase (GO). The reactions that can occur in a glucose test strip aresummarized below in Equations 1 and 2.

Glucose+GO_((ox))→Gluconic Acid+GO_((red))   Eq. 1

GO_((red))+2Fe(CN)₆ ³⁻→GO_((ox))+2Fe(CN)₆ ⁴⁻  Eq. 2

As illustrated in Equation 1, glucose is oxidized to gluconic acid bythe oxidized form of glucose oxidase (GO_((ox))). It should be notedthat GO_((ox)) may also be referred to as an “oxidized enzyme.” Duringthe reaction in Equation 1, the oxidized enzyme GO_((ox)) is convertedto its reduced state, which is denoted as GO_((red)) (i.e., “reducedenzyme”). Next, the reduced enzyme GO_((red)) is re-oxidized back toGO_((ox)) by reaction with Fe(CN)₆ ³⁻ (referred to as either theoxidized mediator or ferricyanide) as illustrated in Equation 2. Duringthe re-generation of GO_((red)) back to its oxidized state GO_((ox)),Fe(CN)₆ ³⁻ is reduced to Fe(CN)₆ ⁴⁻ (referred to as either reducedmediator or ferrocyanide).

When the reactions set forth above are conducted with a test signalapplied between two electrodes, a test current can be created by theelectrochemical re-oxidation of the reduced mediator at the electrodesurface. Thus, since, in an ideal environment, the amount offerrocyanide created during the chemical reaction described above isdirectly proportional to the amount of glucose in the sample positionedbetween the electrodes, the test current generated would be proportionalto the glucose content of the sample. A mediator, such as ferricyanide,is a compound that accepts electrons from an enzyme such as glucoseoxidase and then donates the electrons to an electrode. As theconcentration of glucose in the sample increases, the amount of reducedmediator formed also increases; hence, there is a direct relationshipbetween the test current, resulting from the re-oxidation of reducedmediator, and glucose concentration. In particular, the transfer ofelectrons across the electrical interface results in the flow of a testcurrent (2 moles of electrons for every mole of glucose that isoxidized). The test current resulting from the introduction of glucosecan, therefore, be referred to as a glucose signal.

Electrochemical biosensors may be adversely affected by the presence ofcertain blood components that may undesirably affect the measurement andlead to inaccuracies in the detected signal. This inaccuracy may resultin an inaccurate glucose reading, leaving the patient unaware of apotentially dangerous blood sugar level, for example. As one example,the blood hematocrit level (i.e. the percentage of the amount of bloodthat is occupied by red blood cells) can erroneously affect a resultinganalyte concentration measurement.

Variations in a volume of red blood cells within blood can causevariations in glucose readings measured with disposable electrochemicaltest strips. Typically, a negative bias (i.e., lower calculated analyteconcentration) is observed at high hematocrit, while a positive bias(i.e., higher calculated analyte concentration as compared toreferential analyte concentration) is observed at low hematocrit. Athigh hematocrit, for example, the red blood cells may impede thereaction of enzymes and electrochemical mediators, reduce the rate ofchemistry dissolution since there is less plasma volume to solvate thechemical reactants, and slow diffusion of the mediator. These factorscan result in a lower than expected glucose reading as less signal isproduced during the electrochemical process. Conversely, at lowhematocrit, fewer red blood cells may affect the electrochemicalreaction than expected, and a higher measured signal can result. Inaddition, the physiological fluid sample resistance is also hematocritdependent, which can affect voltage and/or current measurements.

Several strategies have been used to reduce or avoid hematocrit basedvariations on blood glucose. For example, test strips have been designedto incorporate meshes to remove red blood cells from the samples, orhave included various compounds or formulations designed to increase theviscosity of red blood cells and attenuate the effect of low hematocriton concentration determinations. Other test strips have included lysisagents and systems configured to determine hemoglobin concentration inan attempt to correct hematocrit. Further, biosensors have beenconfigured to measure hematocrit by measuring an electrical response ofthe fluid sample via alternating current signals or change in opticalvariations after irradiating the physiological fluid sample with light,or measuring hematocrit based on a function of sample chamber fill time.These sensors have certain disadvantages. A common technique of thestrategies involving detection of hematocrit is to use the measuredhematocrit value to correct or change the measured analyteconcentration, which technique is generally shown and described in thefollowing respective US Patent Application Publication Nos.2010/0283488; 2010/0206749; 2009/0236237; 2010/0276303; 2009/0223834;2008/0083618; 2004/0079652; 2009/0194432; or U.S. Pat. Nos. 7,972,861and 7,258,769, all of which are incorporated by reference herein to thisapplication.

SUMMARY OF THE DISCLOSURE

Applicant has provided various embodiments of a novel technique to allowanalyte measurements to account for the effects of temperature upon theelectrochemical reaction. Advantageously, this new technique has enabledapplicant to provide a technical contribution to the field in thatapproximately 97% of the biosensors fall with ±15 mg/dL for measurementsbelow 100 mg/dL and ±15% for measurements at 100 mg/dL or greater. Anadditional technical contribution is also provided by this invention inthat the average bias to nominal bias is within ±10 mg/dL formeasurements below 100 mg/dL and ±10% for measurements at 100 mg/dL orgreater.

In a first aspect, applicant has devised an analyte measurement systemthat includes a biosensor configured to be coupled to a meter. Thebiosensor has a plurality of electrodes including at least twoelectrodes with an enzyme disposed thereon. The meter includes amicrocontroller coupled to a power source, memory and the plurality ofelectrodes of the biosensor. The microcontroller is configured to:measure ambient temperature proximate the biosensor; drive a signal tothe at least two electrodes when a fluid sample with an analyte isdeposited proximate the at least two electrodes; measure a signal outputfrom the at least two electrodes during the electrochemical reaction;calculate an uncompensated analyte value from the signal output; adjustthe uncompensated analyte value to a final analyte value with atemperature compensation term defined by a relationship in which: (a)the temperature compensation term increases for increasing uncompensatedanalyte values; the temperature compensation term is inversely relatedto the ambient temperature proximate the biosensor from about 5 degreesCelsius to about 22 degrees Celsius; and the temperature compensationterm is about zero for the ambient temperature proximate the biosensorfrom about 22 degrees Celsius to about 45 degrees Celsius. Themicrocontroller is also configured to annunciate the final analytevalue.

In a second aspect, applicant has provided an analyte measurement systemwith a test strip and an analyte meter. The test strip includes asubstrate and a plurality of electrodes connected to respectiveelectrode connectors. The analyte meter includes a housing with a teststrip port connector configured to connect to the respective electrodeconnectors of the test strip, and a microprocessor in electricalcommunication with the test strip port connector to apply electricalsignals or sense electrical signals from the plurality of electrodes.The microprocessor is configured to: (a) sense a temperature of theenvironment proximate the sensor; (b) apply a first signal to theplurality of electrodes so that a physical characteristic of a fluidsample is determined; (c) estimate an analyte concentration based on apredetermined sampling time point during a test sequence; (d) apply asecond signal to the plurality of electrodes at a specified samplingtime point during the test sequence dictated by the determined physicalcharacteristic so that an uncompensated analyte concentration iscalculated from the second signal; and (e) compensate the uncompensatedanalyte concentration with a temperature compensation term that: (i)increases for uncompensated analyte values that are increasing; (ii) isinversely related to the ambient temperature proximate the biosensorfrom about 5 degrees Celsius to about 22 degrees Celsius; and (iii) isabout zero for the ambient temperature proximate the biosensor fromabout 22 degrees Celsius to about 45 degrees Celsius. The microprocessoris configured to annunciate the final analyte value.

In a third aspect, applicant has developed a glucose meter that includesa housing with a test strip port connector disposed on the housing. Thetest strip port connector is configured to connect to respectiveelectrode connectors of a test strip. The meter has means for: (a)sensing a temperature of the environment proximate the housing; (b)determining a specified sampling time based on a sensed or estimatedphysical characteristic of a sample deposited on a plurality ofelectrodes of the test strip, the specified sampling time being at leastone time point or interval referenced from a start of a test sequenceupon deposition of a sample on the test strip; (c) determining anuncompensated analyte concentration based on the specified samplingtime; (d) compensating the uncompensated analyte concentration with atemperature compensation term that: (i) increases for uncompensatedanalyte values that are increasing; (ii) is inversely related to thetemperature of the housing or the environment proximate the biosensorfrom about 5 degrees Celsius to about 22 degrees Celsius; and (iii) isabout zero for the housing or environmental temperature proximate thebiosensor from about 22 degrees Celsius to about 45 degrees Celsius,along with means for annunciating the final analyte value.

In a fourth aspect, applicant has devised a method of adjusting for theeffect of temperature upon a biosensor that has a plurality ofelectrodes with at least two electrodes provided with enzymes thereon.The method can be achieved by: applying a signal to the at least twoelectrodes; initiating an electrochemical reaction between the at leasttwo electrodes and an analyte in a fluid sample to cause atransformation of the analyte into a byproduct; measuring a signaloutput from the at least two electrodes during the electrochemicalreaction; measuring a temperature proximate the biosensor; calculatingan analyte value representative of a quantity of analyte in the fluidsample from the signal output; adjusting the analyte value to a finalanalyte value by a temperature compensation term defined by arelationship where: (a) the temperature compensation term increases forincreasing analyte values; (b) the temperature compensation term isinversely related to the biosensor temperature in a range of about 5degrees Celsius to about 22 degrees Celsius; and (c) the temperaturecompensation term is about zero for the ambient temperature proximatethe biosensor from about 22 degrees Celsius to about 45 degrees Celsius,and annunciating the final value representative of the quantity ofanalyte in the fluid sample.

In a fifth aspect, applicant has designed a method of determining ananalyte concentration from a fluid sample. The method can be achievedby: depositing a fluid sample on a biosensor to start a test sequence;causing the analyte in the sample to undergo an enzymatic reaction;estimating an analyte concentration in the sample; measuring at leastone physical characteristic of the sample; sensing a temperature of theenvironment proximate the biosensor; defining a specified time pointfrom the start of the test sequence to sample output signals of thebiosensor based on the estimated analyte concentration from theestimating step and at least one physical characteristic from themeasuring step; sampling output signals of the biosensor at thespecified time point; determining an uncompensated analyte concentrationfrom the sampled output signals of the biosensor at the specified timepoint; and compensating the uncompensated analyte value to a finalanalyte value with a temperature compensation term defined by arelationship in which: (a) the temperature compensation term increasesfor increasing uncompensated analyte values; (b) the temperaturecompensation term is inversely related to the ambient temperatureproximate the biosensor from about 5 degrees Celsius to about 22 degreesCelsius; and (c) the temperature compensation term is about zero for theambient temperature proximate the biosensor from about 22 degreesCelsius to about 45 degrees Celsius. The method includes annunciatingthe final analyte value.

And for these aspects, the following features may also be utilized invarious combinations with these previously disclosed aspects: therelationship is represented by an equation of the following form:

$G_{F} = \frac{G_{0}}{1 + \frac{\begin{matrix}{{x_{1}\left( {{Temp} - {Temp}_{0}} \right)}^{3} + {x_{2}\left( {{Temp} - {Temp}_{0}} \right)}^{2} +} \\{x_{3}\left( {{Temp} - {Temp}_{0}} \right)}\end{matrix}}{{x_{4}\left( {\log \left( G_{0} \right)} \right)}^{3} + {x_{5}\left( {\log \left( G_{0} \right)} \right)}^{2} + {x_{6}\left( {\log \left( G_{0} \right)} \right)} + 1}}$

Where:

-   -   G_(F) includes the final glucose result;    -   G₀ includes the uncompensated analyte value G glucose result        (must be ≧1);    -   Temp includes the temperature measured by the meter (in ° C.);    -   Temp₀ is about 22° C. (or a nominal temperature); and    -   x₁ is about 4.69e-4, x₂ is about −2.19e-2, x₃ is about 2.80e-1,        x₄ is about 2.99e0, x₅ is about −3.89e1, and x₆ is about 1.32e2.

Alternatively, the relationship is represented by an equation of thefollowing form:

$\begin{matrix}{G_{F} = \frac{G_{0}}{1 + \frac{\begin{matrix}{{x_{1}\left( {{Temp} - {Temp}_{0}} \right)}^{3} + {x_{2}\left( {{Temp} - {Temp}_{0}} \right)}^{2} +} \\{x_{3}\left( {{Temp} - {Temp}_{0}} \right)}\end{matrix}}{\begin{matrix}{{x_{4}\left( {G_{0} - G_{nom}} \right)}^{3} + {x_{5}\left( {G_{0} - G_{nom}} \right)}^{2} +} \\{{x_{6}\left( {G_{0} - G_{nom}} \right)} + x_{7}}\end{matrix}}}} & {{Eq}.\; 9}\end{matrix}$

Where:

-   -   G_(F) includes the final analyte value;    -   G₀ includes the uncompensated analyte value;    -   G_(nominal) includes a nominal analyte value;    -   Temp includes the temperature measured by the meter (in ° C.);    -   Temp₀ includes about 22° C. (or a nominal temperature); and    -   x₁ is about 4.80e-5, x₂ is about −6.90e-3, x₃ is about 2.18e-1,        x₄ is about 9.18e-6, x₅ is about −5.02e-3, x₆ is about 1.18e0,        and x₇ is about 2.41e-2.

In these prior aspects described above, the microcontroller isconfigured to: (a) apply a first signal to the plurality of electrodesso that a physical characteristic of the fluid sample is determined; (b)estimate an analyte concentration based on a predetermined sampling timepoint during a test sequence; (c) apply a second signal to the pluralityof electrodes; (d) measure output signal from the plurality ofelectrodes at a specified sampling time during the test sequencedictated by the determined physical characteristic so that an analyteconcentration is calculated from the output signal of the plurality ofelectrodes, the specified sampling time is calculated using an equationof the form:

SpecifiedSamplingTime=x _(a) H ^(x) ^(b) +x _(c)

Where:

-   -   “SpecifiedSamplingTime” is designated as a time point from the        start of the test sequence at which to sample the output signal        of the test strip,    -   H represents the physical characteristic of the sample;    -   x_(a) represents about 4.3e5;    -   x_(b) represents about −3.9; and    -   x_(c) represents about 4.8.

For these aspects, the microcontroller determines the uncompensatedanalyte concentration with an equation of the form:

$G_{0} = \left\lbrack \frac{I_{T} - {Intercept}}{Slope} \right\rbrack$

Where:

-   -   G₀ represents an uncompensated analyte concentration;    -   I_(T) represents a signal measured at the SpecifiedSamplingTime;    -   Slope represents the value obtained from calibration testing of        a batch of test strips of which this particular strip comes        from; and    -   Intercept represents the value obtained from calibration testing        of a batch of test strips of which this particular strip comes        from.

Also, for the above aspects, the microcontroller determines a specifiedsampling time based on: (a) a physical characteristic of the fluidsample; and (b) an estimated analyte concentration from the sample. Themicrocontroller estimates the analyte concentration with an equation ofthe form:

$G_{est} = \frac{\left( {I_{E} - x_{2}} \right)}{x_{1}}$

Where:

-   -   G_(est) represents the estimated analyte concentration;    -   I_(E) is the signal measured at about 2.5 seconds;    -   x₁ comprises a calibration slope of a particular batch of        biosensors;    -   x₂ comprises a calibration intercept of a particular batch of        biosensors; and

in which the microcontroller determines the uncompensated analyteconcentration with an equation of the form:

$G_{o} = \frac{\left( {I_{s} - x_{4}} \right)}{x_{3}}$

Where:

-   -   G_(O) represents the uncompensated analyte concentration;    -   I_(S) comprises the signal measured at the specified sampling        time;    -   x₃ comprises a calibration slope of a particular batch of        biosensors; and    -   x₄ comprises the intercept of a particular batch of biosensors.

For the prior aspects, the plurality of electrodes comprises at leasttwo electrodes to measure the physical characteristic and at least twoother electrodes to measure the analyte concentration; the at least twoelectrodes and the at least two other electrodes are disposed in thesame chamber provided on the substrate; the at least two electrodes andthe at least two other electrodes are disposed in respective twodifferent chambers provided on the substrate; all of the electrodes aredisposed on the same plane defined by the substrate; a reagent isdisposed proximate the at least two other electrodes and no reagent isdisposed on the at least two electrodes; the final analyte concentrationis determined from the second signal within about 10 seconds of a startof the test sequence; the sampling time point is selected from a look-uptable that includes a matrix in which different qualitative categoriesof the estimated analyte are set forth in the leftmost column of thematrix and different qualitative categories of the measured or estimatedphysical characteristic are set forth in the topmost row of the matrixand the sampling times are provided in the remaining cells of thematrix; the means for determining includes means for applying a firstsignal to the plurality of electrodes so that a batch slope defined by aphysical characteristic of a fluid sample is derived and for applying asecond signal to the plurality of electrodes so that an analyteconcentration is determined based on the derived batch slope and thespecified sampling time; the means for determining includes means forestimating an analyte concentration based on a predetermined samplingtime point from the start of the test sequence and for selecting aspecified sampling time from a matrix of estimated analyte concentrationand sensed or estimated physical characteristic; the means fordetermining includes means for selecting a batch slope based on thesensed or estimated physical characteristic and for ascertaining thespecified sampling time from the batch slope; the applying of the signalcomprises: (a) applying a first signal to the sample to measure aphysical characteristic of the sample; and (b) driving a second signalto the sample to cause an enzymatic reaction of the analyte and thereagent, wherein the calculating step comprises: estimating an analyteconcentration based on a predetermined sampling time point from thestart of the test sequence; selecting a sampling time point from alook-up table having different qualitative categories of the estimatedanalyte and different qualitative categories of the measured orestimated physical characteristic indexed against different samplingtime points; sampling signal output from the sample at the selectedsampling time point; calculating an analyte concentration from measuredoutput signal sampled at said selected sampling time point in accordancewith an equation of the form:

$G_{0} = \left\lbrack \frac{I_{T} - {Intercept}}{Slope} \right\rbrack$

Where:

-   -   G₀ represents an uncompensated analyte concentration;    -   I_(T) represents a signal (proportional to analyte        concentration) measured at the selected sampling time T;    -   Slope represents the value obtained from calibration testing of        a batch of test strips of which this particular strip comes        from; and    -   Intercept represents the value obtained from calibration testing        of a batch of test strips of which this particular strip comes        from.

In the prior aspects, the applying step comprises: (a) applying a firstsignal to the sample to measure a physical characteristic of the fluidsample; and (b) driving a second signal to the sample to cause anenzymatic reaction of the analyte and the reagent, and the calculatingstep comprises: estimating an analyte concentration based on apredetermined sampling time point from the start of the test sequence;selecting a sampling time point based on both the measured or estimatedphysical characteristic and the estimated analyte concentration;sampling signal output from the sample at the selected sampling timepoint; calculating an analyte concentration from measured output signalsampled at said selected sampling time point; the measuring comprisesapplying a first signal to the sample to measure a physicalcharacteristic of the sample; the causing step comprises driving asecond signal to the sample; the measuring comprises evaluating anoutput signal from at least two electrodes of the biosensor at a pointin time after the start of the test sequence, in which the point in timeis set as a function of at least the measured or estimated physicalcharacteristic; and the determining step comprises calculating ananalyte concentration from the measured output signal at said point intime; further comprising estimating an analyte concentration based on apredetermined sampling time point from the start of the test sequence;the defining comprises selecting a defined time point based on both themeasured or estimated physical characteristic and the estimated analyteconcentration; further comprising estimating an analyte concentrationbased on a measurement of the output signal at a predetermined time; thepredetermined time comprises about 2.5 seconds from the start of thetest sequence; the estimating comprises comparing the estimated analyteconcentration and the measured or estimated physical characteristicagainst a look-up table having different respective ranges of analyteconcentration and physical characteristic of the sample indexed againstdifferent sample measurement times so that the point in time formeasurement of the output from the sample of the second signal isobtained for the calculating step; the applying of the first signal andthe driving of the second signal is sequential; the applying of thefirst signal overlaps with the driving of the second signal; theapplying of the first signal comprises directing an alternating signalto the sample so that a physical characteristic of the sample isdetermined from an output of the alternating signal; the applying of thefirst signal comprises directing an electromagnetic signal to the sampleso that a physical characteristic of the sample is determined from anoutput of the electromagnetic signal; the physical characteristiccomprises at least one of viscosity, hematocrit, temperature anddensity; the physical characteristic comprises hematocrit and theanalyte comprises glucose; the directing comprises driving first andsecond alternating signal at different respective frequencies in which afirst frequency is lower than the second frequency; the first frequencyis at least one order of magnitude lower than the second frequency; thefirst frequency comprises any frequency in the range of about 10 kHz toabout 250 kHz; the sampling comprises sampling the signal outputcontinuously at the start of the test sequence until at least about 10seconds after the start; the sampling time point is selected from alook-up table that includes a matrix in which different qualitativecategories of the estimated analyte are set forth in the leftmost columnof the matrix and different qualitative categories of the measured orestimated physical characteristic are set forth in the topmost row ofthe matrix and the sampling times are provided in the remaining cells ofthe matrix.

In the aforementioned aspects of the disclosure, the steps ofdetermining, estimating, calculating, computing, deriving and/orutilizing (possibly in conjunction with an equation) may be performed byan electronic circuit or a processor. These steps may also beimplemented as executable instructions stored on a computer readablemedium; the instructions, when executed by a computer may perform thesteps of any one of the aforementioned methods.

In additional aspects of the disclosure, there are computer readablemedia, each medium comprising executable instructions, which, whenexecuted by a computer, perform the steps of any one of theaforementioned methods.

In additional aspects of the disclosure, there are devices, such as testmeters or analyte testing devices, each device or meter comprising anelectronic circuit or processor configured to perform the steps of anyone of the aforementioned methods.

These and other embodiments, features and advantages will becomeapparent to those skilled in the art when taken with reference to thefollowing more detailed description of the exemplary embodiments of theinvention in conjunction with the accompanying drawings that are firstbriefly described.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate presently preferred embodimentsof the invention, and, together with the general description given aboveand the detailed description given below, serve to explain features ofthe invention (wherein like numerals represent like elements), in which:

FIG. 1A illustrates an analyte measurement system including a meter anda biosensor.

FIG. 1B illustrates yet another analyte measurement system including ameter and a biosensor.

FIG. 2A illustrates in simplified schematic form the components of themeter 200.

FIG. 2B illustrates in simplified schematic form a preferredimplementation of a variation of meter 200.

FIG. 2C is a simplified block diagram of various blocks of the hand-heldtest meter of FIGS. 1A and 1B;

FIG. 2D is a simplified block diagram of a physical characteristicmeasurement block as can be employed in embodiments according to thepresent disclosure;

FIG. 2E is a simplified annotated schematic diagram of a dual low passfilter sub-block as can be employed in embodiments of the presentdisclosure;

FIG. 2F is a simplified annotated schematic diagram of a transimpedanceamplifier (TIA) sub-block as can be employed in embodiments of thepresent disclosure;

FIG. 2G is a simplified annotated schematic block diagram depicting adual low pass filter sub-block, a calibration load sub-block, abiosensor sample cell interface sub-block, a transimpedance amplifiersub-block, an XOR phase shift measurement sub-block and a QuadraturDEMUX phase-shift measurement sub-block as can be employed in a physicalcharacteristic measurement block of embodiments of the presentdisclosure

FIG. 3A(1) illustrates the test strip 100 of the system of FIG. 1 inwhich there are two physical characteristic sensing electrodes upstreamof the measurement electrodes.

FIG. 3A(2) illustrates a variation of the test strip of FIG. 3A(1) inwhich a shielding or grounding electrode is provided for proximate theentrance of the test chamber;

FIG. 3A(3) illustrates a variation of the test strip of FIG. 3A(2) inwhich a reagent area has been extended upstream to cover at least one ofthe physical characteristic sensing electrodes;

FIG. 3A(4) illustrates a variation of test strip 100 of FIGS. 3A(1),3A(2) and 3A(3) in which certain components of the test strip have beenintegrated together into a single unit;

FIG. 3B illustrates a variation of the test strip of FIG. 3A(1), 3A(2),or 3A(3) in which one physical characteristic sensing electrode isdisposed proximate the entrance and the other physical characteristicsensing electrode is at the terminal end of the test cell with themeasurement electrodes disposed between the pair of physicalcharacteristic sensing electrodes.

FIGS. 3C and 3D illustrate variations of FIG. 3A(1), 3A(2), or 3A(3) inwhich the physical characteristic sensing electrodes are disposed nextto each other at the terminal end of the test chamber with themeasurement electrodes upstream of the physical characteristic sensingelectrodes.

FIGS. 3E and 3F illustrates a physical characteristic sensing electrodesarrangement similar to that of FIG. 3A(1), 3A(2), or 3A(3) in which thepair of physical characteristic sensing electrodes are proximate theentrance of the test chamber.

FIG. 4A illustrates a graph of time over applied potential to thebiosensor of FIGS. 3A(1), 3A(2), 3A(3) and 3B-3F.

FIG. 4B illustrates a graph of time over output current from thebiosensor of FIGS. 3A(1), 3A(2), 3A(3) and 3B-3F.

FIG. 5 illustrates an exemplary waveform applied to the test chamber anda waveform as measured from the test chamber to show a time delaybetween the waveforms.

FIG. 6 illustrates a logic diagram of an exemplary method to achieve amore accurate analyte determination.

FIG. 7 illustrates a signal output transient of the biosensor and therange of time point utilized for determination of the analyte, as wellas the estimation of the analyte concentration.

FIG. 8 illustrates data from test measurements conducted with theexemplary technique herein such that the data show the bias of less thanabout ±10% for the hematocrit range of about 30% to about 55%.

FIG. 9 illustrates the temperature compensation factors as applied touncompensated analyte measurements.

FIG. 10 illustrates the results from 24 batches of biosensor where theresults have been compensated to account for temperature effect upon theelectrochemical reaction of the analyte in the fluid sample as comparedto reference values.

FIGS. 11A-11E illustrates the results of the 24 batches and the averagebias to nominal temperatures at varying analyte measurements andenvironmental temperatures.

MODES OF CARRYING OUT THE INVENTION

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are identicallynumbered. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. The detailed description illustrates by way of example, notby way of limitation, the principles of the invention. This descriptionwill clearly enable one skilled in the art to make and use theinvention, and describes several embodiments, adaptations, variations,alternatives and uses of the invention, including what is presentlybelieved to be the best mode of carrying out the invention.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicate a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. More specifically, “about” or“approximately” may refer to the range of values ±10% of the recitedvalue, e.g. “about 90%” may refer to the range of values from 81% to99%. In addition, as used herein, the terms “patient,” “host,” “user,”and “subject” refer to any human or animal subject and are not intendedto limit the systems or methods to human use, although use of thesubject invention in a human patient represents a preferred embodiment.As used herein, “oscillating signal” includes voltage signal(s) orcurrent signal(s) that, respectively, change polarity or alternatedirection of current or are multi-directional. Also used herein, thephrase “electrical signal” or “signal” is intended to include directcurrent signal, alternating signal or any signal within theelectromagnetic spectrum. The terms “processor”; “microprocessor”; or“microcontroller” are intended to have the same meaning and are intendedto be used interchangeably. As used herein, the term “annunciated” andvariations on its root term indicate that an announcement may beprovided via text, audio, visual or a combination of all modes ormediums of communication to a user.

FIG. 1A illustrates a test meter 200 for testing analyte (e.g., glucose)levels in the blood of an individual with a biosensor produced by themethods and techniques illustrated and described herein. Test meter 200may include user interface inputs (206, 210, 214), which can be in theform of buttons, for entry of data, navigation of menus, and executionof commands. Data can include values representative of analyteconcentration, and/or information that are related to the everydaylifestyle of an individual. Information, which is related to theeveryday lifestyle, can include food intake, medication use, theoccurrence of health check-ups, general health condition and exerciselevels of an individual. Test meter 200 can also include a display 204that can be used to report measured glucose levels, and to facilitateentry of lifestyle related information.

Test meter 200 may include a first user interface input 206, a seconduser interface input 210, and a third user interface input 214. Userinterface inputs 206, 210, and 214 facilitate entry and analysis of datastored in the testing device, enabling a user to navigate through theuser interface displayed on display 204. User interface inputs 206, 210,and 214 include a first marking 208, a second marking 212, and a thirdmarking 216, which help in correlating user interface inputs tocharacters on display 204.

Test meter 200 can be turned on by inserting a biosensor 100 (or itsvariants) into a strip port connector 220, by pressing and brieflyholding first user interface input 206, or by the detection of datatraffic across a data port 218. Test meter 200 can be switched off byremoving biosensor 100 (or its variants), pressing and briefly holdingfirst user interface input 206, navigating to and selecting a meter offoption from a main menu screen, or by not pressing any buttons for apredetermined time. Display 104 can optionally include a backlight.

In one embodiment, test meter 200 can be configured to not receive acalibration input for example, from any external source, when switchingfrom a first test strip batch to a second test strip batch. Thus, in oneexemplary embodiment, the meter is configured to not receive acalibration input from external sources, such as a user interface (suchas inputs 206, 210, 214), an inserted test strip, a separate code key ora code strip, data port 218. Such a calibration input is not necessarywhen all of the biosensor batches have a substantially uniformcalibration characteristic. The calibration input can be a set of valuesascribed to a particular biosensor batch. For example, the calibrationinput can include a batch slope and a batch intercept value for aparticular biosensor batch. The calibrations input, such as batch slopeand intercept values, may be preset within the meter as will bedescribed below.

Referring to FIG. 2A, an exemplary internal layout of test meter 200 isshown. Test meter 200 may include a processor 300, which in someembodiments described and illustrated herein is a 32-bit RISCmicrocontroller. In the preferred embodiments described and illustratedherein, processor 300 is preferably selected from the MSP 430 family ofultra-low power microcontrollers manufactured by Texas Instruments ofDallas, Tex. The processor can be bi-directionally connected via I/Oports 314 to a memory 302, which in some embodiments described andillustrated herein is an EEPROM. Also connected to processor 300 via I/Oports 214 are the data port 218, the user interface inputs 206, 210, and214, and a display driver 320. Data port 218 can be connected toprocessor 300, thereby enabling transfer of data between memory 302 andan external device, such as a personal computer. User interface inputs206, 210, and 214 are directly connected to processor 300. Processor 300controls display 204 via display driver 320. Memory 302 may bepre-loaded with calibration information, such as batch slope and batchintercept values, during production of test meter 200. This pre-loadedcalibration information can be accessed and used by processor 300 uponreceiving a suitable signal (such as current) from the strip via stripport connector 220 so as to calculate a corresponding analyte level(such as blood glucose concentration) using the signal and thecalibration information without receiving calibration input from anyexternal source.

In embodiments described and illustrated herein, test meter 200 mayinclude an Application Specific Integrated Circuit (ASIC) 304, so as toprovide electronic circuitry used in measurements of glucose level inblood that has been applied to a test strip 100 (or its variants)inserted into strip port connector 220. Analog voltages can pass to andfrom ASIC 304 by way of an analog interface 306. Analog signals fromanalog interface 306 can be converted to digital signals by an A/Dconverter 316. Processor 300 further includes a core 308, a ROM 310(containing computer code), a RAM 312, and a clock 318. In oneembodiment, the processor 300 is configured (or programmed) to disableall of the user interface inputs except for a single input upon adisplay of an analyte value by the display unit such as, for example,during a time period after an analyte measurement. In an alternativeembodiment, the processor 300 is configured (or programmed) to ignoreany input from all of the user interface inputs except for a singleinput upon a display of an analyte value by the display unit. Detaileddescriptions and illustrations of the meter 200 are shown and describedin International Patent Application Publication No. WO2006070200, whichis hereby incorporated by reference into this application as if fullyset forth herein.

Referring to FIGS. 1B and 2C through 2G, another embodiment of ahand-held test meter 200 is provided. This version of the meter 200includes a display 102, a plurality of user interface buttons 104, astrip port connector 106, a USB interface 108, and a housing. Referringto FIGS. 1B and 2C in particular, hand-held test meter 200 also includesa microcontroller block 112, a physical characteristic measurement block114, a display control block 116, a memory block 118 and otherelectronic components (not shown) for applying a test voltage tobiosensor, and also for measuring an electrochemical response (e.g.,plurality of test current values) and determining an analyte based onthe electrochemical response. To simplify the current descriptions, theFigures do not depict all such electronic circuitry.

Display 102 can be, for example, a liquid crystal display or a bi-stabledisplay configured to show a screen image. An example of a screen imagemay include a glucose concentration, a date and time, an error message,and a user interface for instructing an end user how to perform a test.

Strip port connector 106 is configured to operatively interface with abiosensor 100, such as an electrochemical-based biosensor configured forthe determination of glucose in a whole blood sample. Therefore, thebiosensor is configured for operative insertion into strip portconnector 106 and to operatively interface with phase-shift-basedhematocrit measurement block 114 via, for example, suitable electricalcontacts.

USB Interface 108 can be any suitable interface known to one skilled inthe art. USB Interface 108 is essentially a passive component that isconfigured to power and provide a data line to hand-held test meter 200.

Once a biosensor is interfaced with hand-held test meter 200, or priorthereto, a bodily fluid sample (e.g., a whole blood sample) isintroduced into a sample chamber of the biosensor. The biosensor caninclude enzymatic reagents that selectively and quantitatively transforman analyte into another predetermined chemical form. For example, thebiosensor can include an enzymatic reagent with ferricyanide and glucoseoxidase so that glucose can be physically transformed into an oxidizedform.

Memory block 118 of hand-held test meter 200 includes a suitablealgorithm and can be configured, along with microcontroller block 112 todetermine an analyte based on the electrochemical response of biosensorand the hematocrit of the introduced sample. For example, in thedetermination of the analyte blood glucose, the hematocrit can be usedto compensate for the effect of hematocrit on electrochemicallydetermined blood glucose concentrations.

Microcontroller block 112 is disposed within housing and can include anysuitable microcontroller and/or micro-processer known to those of skillin the art. One such suitable microcontroller is a microcontrollercommercially available from Texas Instruments, Dallas, Tex. USA and partnumber MSP430F5138. This microcontroller can generate a square wave of25 to 250 kHz and a 90-degree phase-shifted wave of the same frequencyand, thereby, function as a signal generation s-block described furtherbelow. MSP430F5138 also has Analog-to-Digital (A/D) processingcapabilities suitable for measuring voltages generated by phase shiftbased hematocrit measurement blocks employed in embodiments of thepresent disclosure.

Referring in particular to FIG. 2D, phase-shift-based hematocritmeasurement block 114 includes a signal generation sub-block 120, a lowpass filter sub-block 122, an biosensor sample cell interface sub-block124, an optional calibration load block 126 (within the dashed lines ofFIG. 2D), a transimpedance amplifier sub-block 128, and a phase detectorsub-block 130.

As described further below, phase-shift-based hematocrit measurementblock 114 and microcontroller block 112 are configured to measure thephase shift of a bodily fluid sample in a sample cell of a biosensorinserted in the hand-held test meter by, for example, measuring thephase shift of one or more high frequency electrical signals driventhrough the bodily fluid sample. In addition, microcontroller block 112is configured to compute the hematocrit of the bodily fluid based on themeasured phase shift. Microcontroller 112 can compute the hematocrit by,for example, employing an A/D converter to measure voltages receivedfrom a phase-detector sub-block, convert the voltages into a phase-shiftand then employing a suitable algorithm or look-up table to convert thephase-shit into a hematocrit value. Once apprised of the presentdisclosure, one skilled in the art will recognize that such an algorithmand/or look-up table will be configured to take into account variousfactors such as strip geometry (including electrode area and samplechamber volume) and signal frequency.

It has been determined that a relationship exists between the reactanceof a whole blood sample and the hematocrit of that sample. Electricalmodeling of a bodily fluid sample (i.e., a whole blood sample) asparallel capacitive and resistive components indicates that when analternating current (AC) signal is forced through the bodily fluidsample, the phase shift of the AC signal will be dependent on both thefrequency of the AC voltage and the hematocrit of the sample. Moreover,modeling indicates that hematocrit has a relatively minor effect on thephase shift when the frequency of the signal is in the range ofapproximately 10 kHz to 25 kHz and a maximum effect on the phase shiftwhen the frequency of the signal is in the range of approximately 250kHz to 500 KHz. Therefore, the hematocrit of a bodily fluid sample canbe measured by, for example, driving AC signals of known frequencythrough the bodily fluid sample and detecting their phase shift. Forexample, the phase-shift of a signal with a frequency in the range of 10kHz to 25 kHz can be used as a reference reading in such a hematocritmeasurement while the phase shift of a signal with a frequency in therange of 250 kHz to 500 kHz can be used as the primary measurement.

Referring to FIGS. 2C-2G, in particular, signal generation sub-block 120can be any suitable signal generation block and is configured togenerate a square wave (0V to Vref) of a desired frequency. Such asignal generation sub-block can, if desired, be integrated intomicrocontroller block 112.

The signal generated by signal generation sub-block 120 l iscommunicated to dual low pass filter sub-block 122, which is configuredto convert the square wave signal to a sine wave signal of apredetermined frequency. The dual LPF of FIG. 2E is configured toprovide both a signal of a first frequency (such as a frequency in therange of 10 kHz to 25 kHz) and a signal of a second frequency (such as afrequency in the range of 250 kHz to 500 kHz) to the biosensor samplecell interface sub-block and a biosensors' sample chamber (also referredto as the HCT measurement cell). Selection of the first and secondfrequency is accomplished using switch IC7 of FIG. 2E. The dual LPF ofFIG. 2E includes employs two suitable operational amplifiers (IC4 andIC5) such as the operational amplifier available from Texas Instruments,Dallas, Tex., USA as high-speed, voltage feedback, CMOS operationalamplifier part number OPA354.

Referring to FIG. 2E, F-DRV represents a square wave input of either alow or high frequency (e.g., 25 kHz or 250 kHz) and is connected to bothIC4 and IC5. Signal Fi-HIGH/LOW (from the microcontroller) selects theoutput of dual low pass filter sub-block 122 via switch IC7. C5 in FIG.2E is configured to block the operating voltage of dual low pass filtersub-block 122 from the HCT measurement cell.

Although a specific dual LPF is depicted in FIG. 2E, dual low passfilter sub-block 122 can be any suitable low pass filter sub-block knownto one skilled in the art including, for example, any suitable multiplefeedback low pass filter, or a Sallen and Key low pass filter.

The sine wave produced by low pass filter sub-block 122 is communicatedto biosensor sample cell interface sub-block 124 where it is drivenacross the sample cell of the biosensor (also referred to as an HCTmeasurement cell). Biosensor sample cell interface block 124 can be anysuitable sample cell interface block including, for example, aninterface block configured to operatively interface with the sample cellof the biosensor via first electrode and second electrodes of thebiosensor disposed in the sample cell. In such a configuration, thesignal can be driven into the sample cell (from the low pass filtersub-block) via the first electrode and picked-up from the sample cell(by the transimpedance amplifier sub-block) via the second electrode asdepicted in FIG. 2G.

The current produced by driving the signal across the sample cell ispicked-up by transimpedance amplifier sub-block 128 and converted into avoltage signal for communication to phase detector sub-block 130.

Transimpedance sub-block 128 can be any suitable transimpedancesub-block known to one skilled in the art. FIG. 2F is a simplifiedannotated schematic block diagram of one such transimpedance amplifiersub-block (based on two OPA354 operational amplifiers, IC3 and IC9). Thefirst stage of TIA sub-block 128 operates at, for example, 400 mV, whichlimits the AC amplitude to +/−400 mV. The second stage of TIA sub-block128 operates at Vref/2, a configuration which enables the generation ofan output of the full span of the microcontroller A/D inputs. C9 of TIAsub-block 128 serves as a blocking component that only allows an AC sinewave signal to pass.

Phase detector sub-block 130 can be any suitable phase detectorsub-block that produces either a digital frequency that can be read backby microcontroller block 112 using a capture function, or an analogvoltage that can be read back by microcontroller block 112 using ananalog to digital converter. FIG. 2G depicts a schematic that includestwo such phase detector sub-blocks, namely an XOR phase detector (in theupper half of FIG. 2G and including IC22 and IC23) and a QuadratureDEMUX phase detector (in the lower half of FIG. 2G and including IC12and IC13).

FIG. 2G also depicts a calibration load sub-block 126 that includes aswitch (IC16) and a dummy load R7 and C6. Calibration load sub-block 126is configured for the dynamic measurement of a phase offset for theknown phase shift of zero degrees produced by resistor R7, thusproviding a phase offset for use in calibration. C6 is configured toforce a predetermined slight phase shift, e.g. to compensate for phasedelays caused by parasitic capacities in the signal traces to the samplecell, or for phase delays in the electrical circuits (LPF and TIA).

The Quadrature DEMUX phase detector circuit of FIG. 2G includes twoportions, one portion for a resistive part of the incoming AC signal andone portion for the reactive portion of the incoming AC signal. Use ofsuch two portions enables the simultaneous measurement of both theresistive and reactive portion of the AC signal and a measurement rangethat covers 0 degrees to 360 degrees. The Quadrature DEMUX circuit ofFIG. 2G generates two separate output voltages. One of these outputvoltages represents the “in phase measurement” and is proportional tothe “resistive” part of the AC signal, the other output voltagerepresents the “Quadrature Measurement” and is proportional to the“reactive part of the signal. The phase shift is calculated as:

Φ=tan⁻¹(V _(QUAD-PHASE) /V _(IN-PHASE))

Such a Quadrature DEMUX phase detector circuit can also be employed tomeasure the impedance of a bodily fluid sample in the sample cell. It ishypothesized, without being bound, that the impedance could be employedalong with the phase-shift, or independently thereof, to determine thehematocrit of the bodily sample. The amplitude of a signal forcedthrough the sample cell can be calculated using the two voltage outputsof the Quadrature DEMUX circuit as follows:

Amplitude=SQR((V _(QUAD-PHASE))²+(V _(IN-PHASE))²)

This amplitude can then be compared to an amplitude measured for theknown resistor of calibration load block 126 to determine the impedance.The XOR phase detector portion has a measurement range of 0° to 180°, oralternatively a measurement range of −90° to +90°, depending whether the“Square wave input from μC” is in phase to the sine wave or is set to a90° phase shift. The XOR phase detector produces an output frequencythat is always double the input frequency, however the duty cyclevaries. If both inputs are perfectly in phase, the output is LOW, ifboth inputs are 180° shifted the output is always HIGH. By integratingthe output signal (e.g. via a simple RC element) a voltage can begenerated that is directly proportional to the phase shift between bothinputs.

As provided herein, one skilled in the art will recognize that phasedetector sub-blocks employed in embodiments of the present disclosurecan take any suitable form and include, for example, forms that employrising edge capture techniques, dual edge capture techniques, XORtechniques and synchronous demodulation techniques.

Since low pass filter sub-block 122, transimpedance amplifier sub-block128 and phase detector sub-block 130 can introduce a residual phaseshift into phase-shift-based hematocrit measurement block 114,calibration load block 126 can be optionally included in thephase-shift-based hematocrit measurement block. Calibration load block126 is configured to be essentially resistive in nature (for example a33k-ohm load) and, therefore, induces no phase shift between excitationvoltage and generated current. Calibration load block 126 is configuredto be switched in across the circuit to give a “zero” calibrationreading. Once calibrated, the hand-held test meter can measure the phaseshift of a bodily fluid sample, subtract the “zero” reading to compute acorrected phase shift and subsequently compute the physicalcharacteristic of the sample based on the corrected phase shift.

FIG. 3A(1) is an exemplary exploded perspective view of a test strip100, which may include seven layers disposed on a substrate 5. The sevenlayers disposed on substrate 5 can be a first conductive layer 50 (whichcan also be referred to as electrode layer 50), an insulation layer 16,two overlapping reagent layers 22 a and 22 b, an adhesive layer 60 whichincludes adhesive portions 24, 26, and 28, a hydrophilic layer 70, and atop layer 80 which forms a cover 94 for the test strip 100. Test strip100 may be manufactured in a series of steps where the conductive layer50, insulation layer 16, reagent layers 22, and adhesive layer 60 aresequentially deposited on substrate 5 using, for example, ascreen-printing process. Note that the electrodes 10, 12, and 14) aredisposed for contact with the reagent layer 22 a and 22 b whereas thephysical characteristic sensing electrodes 19 a and 20 a are spacedapart and not in contact with the reagent layer 22. Hydrophilic layer 70and top layer 80 can be disposed from a roll stock and laminated ontosubstrate 5 as either an integrated laminate or as separate layers. Teststrip 100 has a distal portion 3 and a proximal portion 4 as shown inFIG. 3A(1).

Test strip 100 may include a sample-receiving chamber 92 through which aphysiological fluid sample 95 may be drawn through or deposited (FIG.3A(2)). The physiological fluid sample discussed herein may be blood.Sample-receiving chamber 92 can include an inlet at a proximal end andan outlet at the side edges of test strip 100, as illustrated in FIG.3A(1). A fluid sample 95 can be applied to the inlet along axis L-L(FIG. 3A(2)) to fill a sample-receiving chamber 92 so that glucose canbe measured. The side edges of a first adhesive pad 24 and a secondadhesive pad 26 located adjacent to reagent layer 22 each define a wallof sample-receiving chamber 92, as illustrated in FIG. 3A(1). A bottomportion or “floor” of sample-receiving chamber 92 may include a portionof substrate 5, conductive layer 50, and insulation layer 16, asillustrated in FIG. 3A(1). A top portion or “roof” of sample-receivingchamber 92 may include distal hydrophilic portion 32, as illustrated inFIG. 3A(1). For test strip 100, as illustrated in FIG. 3A(1), substrate5 can be used as a foundation for helping support subsequently appliedlayers. Substrate 5 can be in the form of a polyester sheet such as apolyethylene tetraphthalate (PET) material (Hostaphan PET supplied byMitsubishi). Substrate 5 can be in a roll format, nominally 350 micronsthick by 370 millimeters wide and approximately 60 meters in length.

A conductive layer is required for forming electrodes that can be usedfor the electrochemical measurement of glucose. First conductive layer50 can be made from a carbon ink that is screen-printed onto substrate5. In a screen-printing process, carbon ink is loaded onto a screen andthen transferred through the screen using a squeegee. The printed carbonink can be dried using hot air at about 140° C. The carbon ink caninclude VAGH resin, carbon black, graphite (KS15), and one or moresolvents for the resin, carbon and graphite mixture. More particularly,the carbon ink may incorporate a ratio of carbon black: VAGH resin ofabout 2.90:1 and a ratio of graphite: carbon black of about 2.62:1 inthe carbon ink.

For test strip 100, as illustrated in FIG. 3A(1), first conductive layer50 may include a reference electrode 10, a first working electrode 12, asecond working electrode 14, third and fourth physical characteristicsensing electrodes 19 a and 19 b, a first contact pad 13, a secondcontact pad 15, a reference contact pad 11, a first working electrodetrack 8, a second working electrode track 9, a reference electrode track7, and a strip detection bar 17. The physical characteristic sensingelectrodes 19 a and 20 a are provided with respective electrode tracks19 b and 20 b. The conductive layer may be formed from carbon ink. Firstcontact pad 13, second contact pad 15, and reference contact pad 11 maybe adapted to electrically connect to a test meter. First workingelectrode track 8 provides an electrically continuous pathway from firstworking electrode 12 to first contact pad 13. Similarly, second workingelectrode track 9 provides an electrically continuous pathway fromsecond working electrode 14 to second contact pad 15. Similarly,reference electrode track 7 provides an electrically continuous pathwayfrom reference electrode 10 to reference contact pad 11. Strip detectionbar 17 is electrically connected to reference contact pad 11. Third andfourth electrode tracks 19 b and 20 b connect to the respectiveelectrodes 19 a and 20 a. A test meter can detect that test strip 100has been properly inserted by measuring a continuity between referencecontact pad 11 and strip detection bar 17, as illustrated in FIG. 3A(1).

Variations of the test strip 100 (FIG. 3A(1), 3A(2), 3A(3), or 3A(4))are shown in FIGS. 3B-3F. Briefly, with regard to variations of teststrip 100 (illustrated exemplarily in FIGS. 3A(2), 3A(2)), these teststrips include an enzymatic reagent layer disposed on the workingelectrode, a patterned spacer layer disposed over the first patternedconductive layer and configured to define a sample chamber within thebiosensor, and a second patterned conductive layer disposed above thefirst patterned conductive layer. The second patterned conductive layerincludes a first phase-shift measurement electrode and a secondphase-shift measurement electrode. Moreover, the first and secondphase-shift measurement electrodes are disposed in the sample chamberand are configured to measure, along with the hand-held test meter, aphase shift of an electrical signal forced through a bodily fluid sampleintroduced into the sample chamber during use of the biosensor. Suchphase-shift measurement electrodes are also referred to herein as bodilyfluid phase-shift measurement electrodes. Biosensors of variousembodiments described herein are believed to be advantageous in that,for example, the first and second phase-shift measurement electrodes aredisposed above the working and reference electrodes, thus enabling asample chamber of advantageously low volume. This is in contrast to aconfiguration wherein the first and second phase-shift measurementelectrodes are disposed in a co-planar relationship with the working andreference electrodes thus requiring a larger bodily fluid sample volumeand sample chamber to enable the bodily fluid sample to cover the firstand second phase-shift measurement electrodes as well as the working andreference electrodes.

In the embodiment of FIG. 3A(2) which is a variation of the test stripof FIG. 3A(1), an additional electrode 10 a is provided as an extensionof any of the plurality of electrodes 19 a, 20 a, 14, 12, and 10. Itmust be noted that the built-in shielding or grounding electrode 10 a isused to reduce or eliminate any capacitance coupling between the fingeror body of the user and the characteristic measurement electrodes 19 aand 20 a. The grounding electrode 10 a allows for any capacitance to bedirected away from the sensing electrodes 19 a and 20 a. To do this, thegrounding electrode 10 a can be connected any one of the other fiveelectrodes or to its own separate contact pad (and track) for connectionto ground on the meter instead of one or more of contact pads 15, 17, 13via respective tracks 7, 8, and 9. In a preferred embodiment, thegrounding electrode 10 a is connected to one of the three electrodesthat has reagent 22 disposed thereon. In a most preferred embodiment,the grounding electrode 10 a is connected to electrode 10. Being thegrounding electrode, it is advantageous to connect the groundingelectrode to the reference electrode (10) so not to contribute anyadditional current to the working electrode measurements which may comefrom background interfering compounds in the sample. Further byconnecting the shield or grounding electrode 10 a to electrode 10 thisis believed to effectively increase the size of the counter electrode 10which can become limiting especially at high signals. In the embodimentof FIG. 3A(2), the reagent are arranged so that they are not in contactwith the measurement electrodes 19 a and 20 a. Alternatively, in theembodiment of FIG. 3A(3), the reagent 22 is arranged so that the reagent22 contacts at least one of the sensing electrodes 19 a and 20 a.

In alternate version of test strip 100, shown here in FIG. 3A(4), thetop layer 38, hydrophilic film layer 34 and spacer 29 have been combinedtogether to form an integrated assembly for mounting to the substrate 5with reagent layer 22′ disposed proximate insulation layer 16′.

In the embodiment of FIG. 3B, the analyte measurement electrodes 10, 12,and 14 are disposed in generally the same configuration as in FIG.3A(1), 3A(2), or 3A(3). The electrodes 19 a and 20 a to sense physicalcharacteristic (e.g., hematocrit) level, however, are disposed in aspaced apart configuration in which one electrode 19 a is proximate anentrance 92 a to the test chamber 92 and another electrode 20 a is atthe opposite end of the test chamber 92. Electrodes 10, 12, and 14 aredisposed to be in contact with a reagent layer 22.

In FIGS. 3C, 3D, 3E and 3F, the physical characteristic (e.g.,hematocrit) sensing electrodes 19 a and 20 a are disposed adjacent eachother and may be placed at the opposite end 92 b of the entrance 92 a tothe test chamber 92 (FIGS. 3C and 3D) or adjacent the entrance 92 a(FIGS. 3E and 3F). In all of these embodiments, the physicalcharacteristic sensing electrodes are spaced apart from the reagentlayer 22 so that these physical characteristic sensing electrodes arenot impacted by the electrochemical reaction of the reagent in thepresence of a fluid sample (e.g., blood or interstitial fluid)containing glucose.

In the various embodiments of the biosensor, there are two measurementsthat are made to a fluid sample deposited on the biosensor. Onemeasurement is that of the concentration of the analyte (e.g. glucose)in the fluid sample while the other is that of physical characteristic(e.g., hematocrit) in the same sample. The measurement of the physicalcharacteristic (e.g., hematocrit) is used to modify or correct theglucose measurement so as to remove or reduce the effect of red bloodcells on the glucose measurements. Both measurements (glucose andhematocrit) can be performed in sequence, simultaneously or overlappingin duration. For example, the glucose measurement can be performed firstthen the physical characteristic (e.g., hematocrit); the physicalcharacteristic (e.g., hematocrit) measurement first then the glucosemeasurement; both measurements at the same time; or a duration of onemeasurement may overlap a duration of the other measurement. Eachmeasurement is discussed in detail as follow with respect to FIGS. 4A,4B and 5.

FIG. 4A is an exemplary chart of a test signal applied to test strip 100and its variations shown here in FIGS. 3A-3T. Before a fluid sample isapplied to test strip 100 (or its variants), test meter 200 is in afluid detection mode in which a first test signal of about 400millivolts is applied between second working electrode and referenceelectrode. A second test signal of about 400 millivolts is preferablyapplied simultaneously between first working electrode (e.g., electrode12 of strip 100) and reference electrode (e.g., electrode 10 of strip100). Alternatively, the second test signal may also be appliedcontemporaneously such that a time interval of the application of thefirst test signal overlaps with a time interval in the application ofthe second test voltage. The test meter may be in a fluid detection modeduring fluid detection time interval TFD prior to the detection ofphysiological fluid at starting time at zero. In the fluid detectionmode, test meter 200 determines when a fluid is applied to test strip100 (or its variants) such that the fluid wets either the first workingelectrode 12 or second working electrode 14 (or both working electrodes)with respect to reference electrode 10. Once test meter 200 recognizesthat the physiological fluid has been applied because of, for example, asufficient increase in the measured test current at either or both offirst working electrode 12 and second working electrode 14, test meter200 assigns a zero second marker at zero time “0” and starts the testtime interval T_(S). Test meter 200 may sample the current transientoutput at a suitable sampling rate, such as, for example, every 1milliseconds to every 100 milliseconds. Upon the completion of the testtime interval T_(S), the test signal is removed. For simplicity, FIG. 4Aonly shows the first test signal applied to test strip 100 (or itsvariants).

Hereafter, a description of how analyte (e.g., glucose) concentration isdetermined from the known signal transients (e.g., the measuredelectrical signal response in nanoamperes as a function of time) thatare measured when the test voltages of FIG. 4A are applied to the teststrip 100 (or its variants).

In FIG. 4A, the first and second test voltages applied to test strip 100(or its variants described herein) are generally from about +100millivolts to about +600 millivolts. In one embodiment in which theelectrodes include carbon ink and the mediator includes ferricyanide,the test signal is about +400 millivolts. Other mediator and electrodematerial combinations will require different test voltages, as is knownto those skilled in the art. The duration of the test voltages isgenerally from about 1 to about 5 seconds after a reaction period and istypically about 3 seconds after a reaction period. Typically, testsequence time T_(S) is measured relative to time to. As the voltage 401is maintained in FIG. 4A for the duration of T_(S), output signals aregenerated, shown here in FIG. 4B with the current transient 702 for thefirst working electrode 12 being generated starting at zero time andlikewise the current transient 704 for the second working electrode 14is also generated with respect to the zero time. It is noted that whilethe signal transients 702 and 704 have been placed on the samereferential zero point for purposes of explaining the process, inphysical term, there is a slight time differential between the twosignals due to fluid flow in the chamber towards each of the workingelectrodes 12 and 14 along axis L-L. However, the current transients aresampled and configured in the microcontroller to have the same starttime. In FIG. 4B, the current transients build up to a peak proximatepeak time Tp at which time, the current slowly drops off untilapproximately one of 2.5 seconds or 5 seconds after zero time. At thepoint 706, approximately at 5 seconds, the output signal for each of theworking electrodes 12 and 14 may be measured and added together.Alternatively, the signal from only one of the working electrodes 12 and14 can be doubled.

Referring back to FIG. 2B, the system drives a signal to measure orsample the output signals I_(E) from at least one the working electrodes(12 and 14) at any one of a plurality of time points or positions T₁,T₂, T₃, . . . , T_(N). As can be seen in FIG. 4B, the time position canbe any time point or interval in the test sequence T_(S). For example,the time position at which the output signal is measured can be a singletime point T_(1.5) at 1.5 seconds or an interval 708 (e.g., interval˜10milliseconds or more depending on the sampling rate of the system)overlapping the time point T_(2.8) proximate 2.8 seconds.

From knowledge of the parameters of the biosensor (e.g., batchcalibration code offset and batch slope) for the particular test strip100 and its variations, the analyte (e.g., glucose) concentration can becalculated. Output transient 702 and 704 can be sampled to derivesignals I_(E) (by summation of each of the current I_(WE1) and I_(WE2)or doubling of one of I_(WE1) or I_(WE2)) at various time positionsduring the test sequence. From knowledge of the batch calibration codeoffset and batch slope for the particular test strip 100, the analyte(e.g., glucose) concentration can be calculated.

It is noted that “Intercept” and “Slope” are the values obtained bymeasuring calibration data from a batch of biosensors. Typically, around1500 biosensors are selected at random from the lot or batch.Physiological fluid (e.g., blood) from donors is spiked to variousanalyte levels, typically six different glucose concentrations.Typically, blood from 12 different donors is spiked to each of the sixlevels. Eight biosensors (or strips in this embodiment) are given bloodfrom identical donors and levels so that a total of 12×6×8=576 tests areconducted for that lot. These are benchmarked against actual analytelevel (e.g., blood glucose concentration) by measuring these using astandard laboratory analyzer such as Yellow Springs Instrument (YSI). Agraph of measured glucose concentration is plotted against actualglucose concentration (or measured current versus YSI current) and aformula y=mx+c least squares fitted to the graph to give a value forbatch slope m and batch intercept c for the remaining strips from thelot or batch. The applicants have also provided methods and systems inwhich the batch slope is derived during the determination of an analyteconcentration. The “batch slope”, or “Slope”, may therefore be definedas the measured or derived gradient of the line of best fit for a graphof measured glucose concentration plotted against actual glucoseconcentration (or measured current versus YSI current). The “batchintercept”, or “Intercept”, may therefore be defined as the point atwhich the line of best fit for a graph of measured glucose concentrationplotted against actual glucose concentration (or measured current versusYSI current) meets the y axis.

It is worthwhile here to note that the various components, systems andprocedures described earlier allow for applicant to provide an analytemeasurement system that heretofore was not available in the art. Inparticular, this system includes a biosensor that has a substrate and aplurality of electrodes connected to respective electrode connectors.The system further includes an analyte meter 200 that has a housing, atest strip port connector configured to connect to the respectiveelectrode connectors of the test strip, and a microcontroller 300, shownhere in FIG. 2B. The microcontroller 300 is in electrical communicationwith the test strip port connector 220 to apply electrical signals orsense electrical signals from the plurality of electrodes.

Referring to FIG. 2B, details of a preferred implementation of meter 200where the same numerals in FIGS. 2A and 2B have a common description. InFIG. 2B, a strip port connector 220 is connected to the analogueinterface 306 by five lines including an impedance sensing line EIC toreceive signals from physical characteristic sensing electrode(s),alternating signal line AC driving signals to the physicalcharacteristic sensing electrode(s), reference line for a referenceelectrode, and signal sensing lines from respective working electrode 1and working electrode 2. A strip detection line 221 can also be providedfor the connector 220 to indicate insertion of a test strip. The analoginterface 306 provides four inputs to the processor 300: (1) realimpedance Z′; (2) imaginary impedance Z″; (3) signal sampled or measuredfrom working electrode 1 of the biosensor or I_(we1); (4) signal sampledor measured from working electrode 2 of the biosensor or I_(we2). Thereis one output from the processor 300 to the interface 306 to drive anoscillating signal AC of any value from 25 kHz to about 250 kHz orhigher to the physical characteristic sensing electrodes. A phasedifferential P (in degrees) can be determined from the real impedance Z′and imaginary impedance Z″ where:

P=tan⁻¹ {Z″/Z′}  Eq. 3.1

and magnitude M (in ohms and conventionally written as |Z|) from line Z′and Z″ of the interface 306 can be determined where

M=√{square root over ((Z′)²+(Z″)²)}  Eq. 3.2

In this system, the microprocessor is configured to: (a) apply a firstsignal to the plurality of electrodes so that a batch slope defined by aphysical characteristic of a fluid sample is derived and (b) apply asecond signal to the plurality of electrodes so that an analyteconcentration is determined based on the derived batch slope. For thissystem, the plurality of electrodes of the test strip or biosensorincludes at least two electrodes to measure the physical characteristicand at least two other electrodes to measure the analyte concentration.For example, the at least two electrodes and the at least two otherelectrodes are disposed in the same chamber provided on the substrate.Alternatively, the at least two electrodes and the at least two otherelectrodes are disposed in respective two different chambers provided onthe substrate. It is noted that for some embodiments, all of theelectrodes are disposed on the same plane defined by the substrate. Inparticular, in some of the embodiments described herein, a reagent isdisposed proximate the at least two other electrodes and no reagent isdisposed on the at least two electrodes. One feature of note in thissystem is the ability to provide for an accurate analyte measurementwithin about 10 seconds of deposition of a fluid sample (which may be aphysiological sample) onto the biosensor as part of the test sequence.

As an example of an analyte calculation (e.g., glucose) for strip 100(FIG. 3A(1), 3A(2), or 3A(3) and its variants in FIGS. 3B-3T), it isassumed in FIG. 4B that the sampled signal value at 706 for the firstworking electrode 12 is about 1600 nanoamperes whereas the signal valueat 706 for the second working electrode 14 is about 1300 nanoamperes andthe calibration code of the test strip indicates that the Intercept isabout 500 nanoamperes and the Slope is about 18 nanoamperes/mg/dL.Glucose concentration G₀ can be thereafter be determined from Equation3.3 as follow:

G ₀=[(I _(E))−Intercept]/Slope   Eq. 3.3

Where:

-   -   I_(E) is a signal (proportional to analyte concentration) which        is the total signal from all of the electrodes in the biosensor        (e.g., for sensor 100, both electrodes 12 and 14 (or        I_(we1)+I_(we2)));    -   I_(we1) is the signal measured for the first working electrode        at the set sampling time;    -   I_(we2) is the signal measured for the second working electrode        at the set sampling time;    -   Slope is the value obtained from calibration testing of a batch        of test strips of which this particular strip comes from;    -   Intercept is the value obtained from calibration testing of a        batch of test strips of which this particular strip comes from.

From Eq. 3.3; G₀=[(1600+1300)−500]/18 and therefore, G₀=133.33nanoamp˜133 mg/dL.

It is noted here that although the examples have been given in relationto a biosensor 100 which has two working electrodes (12 and 14 in FIG.3A(1)) such that the measured currents from respective workingelectrodes have been added together to provide for a total measuredcurrent I_(E), the signal resulting from only one of the two workingelectrodes can be multiplied by two in a variation of test strip 100where there is only one working electrode (either electrode 12 or 14).Instead of a total signal, an average of the signal from each workingelectrode can be used as the total measured current I_(E) for Equations3.3, 6, and 5-7 described herein, and of course, with appropriatemodification to the operational coefficients (as known to those skilledin the art) to account for a lower total measured current I_(E) than ascompared to an embodiment where the measured signals are added together.Alternatively, the average of the measured signals can be multiplied bytwo and used as I_(E) in Equations 3.3, 6, and 5-7 without the necessityof deriving the operational coefficients as in the prior example. It isnoted that the analyte (e.g., glucose) concentration here is notcorrected for any physical characteristic (e.g., hematocrit value) andthat certain offsets may be provided to the signal values I_(we1) andI_(we2) to account for errors or delay time in the electrical circuit ofthe meter 200. Temperature compensation can also be utilized to ensurethat the results are calibrated to a referential temperature such as forexample room temperature of about 20 degrees Celsius.

Now that an analyte (e.g., glucose) concentration (G₀) can be determinedfrom the signal I_(E), a description of applicant's technique todetermine the physical characteristic (e.g., hematocrit) of the fluidsample is provided in relation to FIG. 5. In FIG. 5, the system 200(FIG. 2) applies a first oscillating input signal 800 at a firstfrequency (e.g., of about 25 kilo-Hertz) to a pair of sensingelectrodes. The system is also set up to measure or detect a firstoscillating output signal 802 from the third and fourth electrodes,which in particular involve measuring a first time differential Δt₁between the first input and output oscillating signals. At the same timeor during overlapping time durations, the system may also apply a secondoscillating input signal (not shown for brevity) at a second frequency(e.g., about 100 kilo-Hertz to about 1 MegaHertz or higher, andpreferably about 250 kilo Hertz) to a pair of electrodes and thenmeasure or detect a second oscillating output signal from the third andfourth electrodes, which may involve measuring a second timedifferential Δt₂ (not shown) between the first input and outputoscillating signals. From these signals, the system estimates a physicalcharacteristic (e.g., hematocrit) of the fluid sample based on the firstand second time differentials Δt₁ and Δt₂. Thereafter, the system isable to derive a glucose concentration. The estimate of the physicalcharacteristic (e.g., hematocrit) can be done by applying an equation ofthe form

$\begin{matrix}{{HCT}_{EST} = \frac{\left( {{C_{1}\Delta \; t_{1}} - {C_{2}\Delta \; t_{2}} - C_{3}} \right)}{m_{1}}} & {{Eq}.\mspace{14mu} 4.1}\end{matrix}$

Where:

-   -   each of C₁, C₂, and C₃ is an operational constant for the test        strip and    -   m₁ represent a parameter from regressions data.

Details of this exemplary technique can be found in Provisional U.S.Patent Application Ser. No. 61/530,795 filed on Sep. 2, 2011, entitled,“Hematocrit Corrected Glucose Measurements for Electrochemical TestStrip Using Time Differential of the Signals” with Attorney Docket No.DDI-5124USPSP, which is hereby incorporated by reference.

Another technique to determine physical characteristic (e.g.,hematocrit) can be by two independent measurements of physicalcharacteristic (e.g., hematocrit). This can be obtained by determining:(a) the impedance of the fluid sample at a first frequency and (b) thephase angle of the fluid sample at a second frequency substantiallyhigher than the first frequency. In this technique, the fluid sample ismodeled as a circuit having unknown reactance and unknown resistance.With this model, an impedance (as signified by notation “|Z|”) formeasurement (a) can be determined from the applied voltage, the voltageacross a known resistor (e.g., the intrinsic strip resistance), and thevoltage across the unknown impedance Vz; and similarly, for measurement(b) the phase angle can be measured from a time difference between theinput and output signals by those skilled in the art. Details of thistechnique is shown and described in pending provisional patentapplication Ser. No. 61/530,808 filed Sep. 2, 2011 (Attorney Docket No.DDI5215PSP), which is incorporated by reference. Other suitabletechniques for determining the physical characteristic (e.g.,hematocrit, viscosity, temperature or density) of the fluid sample canalso be utilized such as, for example, U.S. Pat. No. 4,919,770, U.S.Pat. No. 7,972,861, US Patent Application Publication Nos. 2010/0206749,2009/0223834, or “Electric Cell—Substrate Impedance Sensing (ECIS) as aNoninvasive Means to Monitor the Kinetics of Cell Spreading toArtificial Surfaces” by Joachim Wegener, Charles R. Keese, and IvarGiaever and published by Experimental Cell Research 259, 158-166 (2000)doi:10.1006/excr.2000.4919, available online athttp://www.idealibrary.coml; “Utilization of AC Impedance Measurementsfor Electrochemical Glucose Sensing Using Glucose Oxidase to ImproveDetection Selectivity” by Takuya Kohma, Hidefumi Hasegawa, DaisukeOyamatsu, and Susumu Kuwabata and published by Bull. Chem. Soc. Jpn.Vol. 80, No. 1, 158-165 (2007), all of these documents are incorporatedby reference.

Another technique to determine the physical characteristic (e.g.,hematorcrits, density, or temperature) can be obtained by knowing thephase difference (e.g., phase angle) and magnitude of the impedance ofthe sample. In one example, the following relationship is provided forthe estimate of the physical characteristic or impedance characteristicof the sample (“IC”):

IC=M ² *y ₁ +M*y ₂ +y ₃ +P ² *y ₄ +P*y ₅   Eq. 4.2

Where:

-   -   M represents a magnitude |Z| of a measured impedance in ohms);    -   P represents a phase difference between the input and output        signals (in degrees);    -   y₁ is about −3.2e-08 and ±10%, 5% or 1% of the numerical value        provided hereof (and depending on the frequency of the input        signal, can be zero);    -   y₂ is about 4.1e-03 and ±10%, 5% or 1% of the numerical value        provided hereof (and depending on the frequency of the input        signal, can be zero);    -   y₃ is about −2.5e+01 and ±10%, 5% or 1% of the numerical value        provided hereof;    -   y₄ is about 1.5e-01 and ±10%, 5% or 1% of the numerical value        provided hereof (and depending on the frequency of the input        signal, can be zero); and    -   y₅ is about 5.0 and ±10%, 5% or 1% of the numerical value        provided hereof (and depending on the frequency of the input        signal, can be zero).

It is noted here that where the frequency of the input AC signal is high(e.g., greater than 75 kHz) then the parametric terms y₁ and y₂ relatingto the magnitude of impedance M may be ±200% of the exemplary valuesgiven herein such that each of the parametric terms may include zero oreven a negative value. On the other hand, where the frequency of the ACsignal is low (e.g., less than 75 kHz), the parametric terms y₄ and y₅relating to the phase angle P may be ±200% of the exemplary values givenherein such that each of the parametric terms may include zero or even anegative value. It is noted here that a magnitude of H or HCT, as usedherein, is generally equal to the magnitude of IC. In one exemplaryimplementation, H or HCT is equal to IC as H or HCT is used herein thisapplication.

In another alternative implementation, Equation 4.3 is provided.Equation 4.3 is the exact derivation of the quadratic relationship,without using phase angles as in Equation 4.2.

$\begin{matrix}{{IC} = \frac{{- y_{2}} + {\sqrt{y_{2}^{2} - \left( {4\; {y_{3}\left( {y_{1} - M} \right)}} \right)}}}{2\; y_{1}}} & {{Eq}.\mspace{14mu} 4.3}\end{matrix}$

Where:

-   -   IC is the Impedance Characteristic [%];    -   M is the magnitude of impedance [Ohm];    -   y₁ is about 1.2292e1 and ±10%, 5% or 1% of the numerical value        provided hereof;    -   y₂ is about −4.3431e2 and ±10%, 5% or 1% of the numerical value        provided hereof;    -   y₃ is about 3.5260e4 and ±10%, 5% or 1% of the numerical value        provided hereof.

By virtue of the various components, systems and insights providedherein, a technique to achieve a temperature compensated analytemeasurement can be understood with reference to FIG. 6. This techniqueinvolves depositing a fluid sample (which may be a physiological sample)on a biosensor at step 604 (e.g., in the form of a test strip as show inFIGS. 3A(1), 3A(2), 3A(3) through 3F) that has been inserted into ameter (step 602). Once the meter 200 is turned on, a signal is appliedto the strip 100 (or its variants) and when the sample is deposited ontothe test chamber, the applied signal physically transforms the analyte(e.g., glucose) in the sample into a different physical form (e.g.,gluconic acid) due to the enzymatic reaction of the analyte with thereagent in the test chamber. As the sample flows into the capillarychannel of the test cell, at least one physical characteristic of thesample is obtained (step 608) along with estimate of the analyteconcentration (step 610). From the obtained physical characteristic(step 608) and estimated analyte concentration (step 610), a samplingtime point is defined (at step 612) at which the signal output from thesample during the test sequence is measured (at step 614) and used forcalculating the analyte concentration in step 616. In particular, thestep of obtaining the physical characteristic (step 608) may includeapplying a first signal to the sample to measure a physicalcharacteristic of the sample, while the step 606 of initiating anenzymatic reaction may involve driving a second signal to the sample,and the step of measuring (step 614) may entail evaluating an outputsignal from the at least two electrodes at a point in time after thestart of the test sequence, in which the point in time is set (at step612) as a function of at least the measured or estimated physicalcharacteristic (step 608) and estimated analyte concentration (step610).

The determination of the appropriate point (or time interval) during thetest sequence T_(S) as a function of the measured or estimated physicalcharacteristic(s) (in step 612) can be determined by the use of alook-up table programmed into the microprocessor of the system. Forexample, a look-up table may be provided that allows for the system toselect the appropriate sampling time for the analyte (e.g., glucose orketone) with measured or known physical characteristic (e.g., hematocritor viscosity) of the sample.

In particular, an appropriate sampling time point may be based on anearly estimation of the analyte and the measured or known physicalcharacteristic to arrive at the appropriate sampling time that gives thelowest error or bias as compared to referential values. In thistechnique, a look up table is provided in which the defined samplingtime point is correlated to (a) the estimated analyte concentration and(b) the physical characteristic of the sample. For example, Table 1 maybe programmed into the meter to provide a matrix in which qualitativecategories (low, medium, and high glucose) of the estimated analyte formthe main column and the qualitative categories (low, medium, and high)of the measured or estimated physical characteristic form the headerrow. In the second column, t/Hct is a value determined experimentally ofthe time shift per % hematocrit difference from nominal hematocrit of42%. As one example, for 55% hematocrit at “Mid-Glucose” would indicatea time shift of (42−55)*90=−1170 ms. The time of −1170 milliseconds isadded to the original test time of about 5000 milliseconds giving(5000−1170=3830 milliseconds)˜3.9 seconds.

TABLE 1 Sampling Time Sampling Sampling Point T for Lo Time Point T TimePoint T Hct (from for Mid Hct for High Hct start of test (from start of(from start of Estimated t/Hct (in sequence, test sequence, testsequence, Analyte milliseconds) in seconds) in seconds) in seconds)Lo-Glucose 40 5.5 5 4.5 Mid-Glucose 90 6.1 5 3.9 Hi-Glucose 110  6.3 53.6

The time T (i.e., a specified sampling time) at which the system shouldbe sampling or measuring the output signal of the biosensor is based onboth the qualitative category of the estimated analyte and measured orestimated physical characteristic and is predetermined based onregression analysis of a large sample size of actual physiological fluidsamples. Applicants note that the appropriate sampling time is measuredfrom the start of the test sequence but any appropriate datum may beutilized in order to determine when to sample the output signal. As apractical matter, the system can be programmed to sample the outputsignal at an appropriate time sampling interval during the entire testsequence such as for example, one sampling every 100 milliseconds oreven as little as about 1 milliseconds. By sampling the entire signaloutput transient during the test sequence, the system can perform all ofthe needed calculations near the end of the test sequence rather thanattempting to synchronize the sampling time with the set time point,which may introduce timing errors due to system delay.

Applicant hereafter will discuss the look-up Table 1 in relation to theparticular analyte of glucose in physiological fluid samples.Qualitative categories of blood glucose are defined in the first columnof Table 1 in which low blood glucose concentrations of less than about70 mg/dL are designated as “Lo-Glucose”; blood glucose concentrations ofhigher than about 70 mg/dL but less than about 250 mg/dL are designatedas “Mid-Glucose”; and blood glucose concentrations of higher than about250 mg/dL are designated as “Hi-Glucose”.

During a test sequence, an “Estimated Analyte” can be obtained bysampling the signal at a convenient time point, typically at fiveseconds during a typical 10 seconds test sequence. The measurementsampled at this five second time point allows for an accurate estimateof the analyte (in this case blood glucose). The system may then referto a look-up table (e.g., Table 1) to determine when to measure thesignal output from the test chamber at a specified sampling time T basedon two criteria: (a) estimated analyte and (b) qualitative value of thephysical characteristic of the sample. For criteria (b), the qualitativevalue of the physical characteristic is broken down into threesub-categories of Low Hct, Mid Hct and High Hct. Thus, in the event thatthe measured or estimated physical characteristic (e.g., hematocrit) ishigh (e.g., greater than 46%) and the estimated glucose is also high,then according to Table 1, the test time for the system to measure thesignal output of test chamber would be about 3.6 seconds. On the otherhand, if the measured hematocrit is low (e.g., less than 38%) and theestimated glucose is low then according to Table 1, the test time T forthe system to measure the signal output of test chamber would be about5.5 seconds.

Once the signal output I_(T) of the test chamber is measured at thedesignated time (which is governed by the measured or estimated physicalcharacteristic), the signal I_(T) is thereafter used in the calculationof the analyte concentration (in this case glucose) with Equation 5below.

$\begin{matrix}{G_{0} = \left\lbrack \frac{I_{T} - {Intercept}}{Slope} \right\rbrack} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

Where:

-   -   G₀ represents an analyte concentration;    -   I_(T) represents a signal (proportional to analyte        concentration) determined from the sum of the end signals        measured at a specified sampling time T, which may be the total        current measured at the specified sampling time T;    -   Slope represents the value obtained from calibration testing of        a batch of test strips of which this particular strip comes from        and is typically about 0.02; and    -   Intercept represents the value obtained from calibration testing        of a batch of test strips of which this particular strip comes        from and is typically from about 0.6 to about 0.7.

It should be noted that the step of applying the first signal and thedriving of the second signal is sequential in that the order may be thefirst signal then the second signal or both signals overlapping insequence; alternatively, the second signal first then the first signalor both signals overlapping in sequence. Alternatively, the applying ofthe first signal and the driving of the second signal may take placesimultaneously.

In the method, the step of applying of the first signal involvesdirecting an alternating signal provided by an appropriate power source(e.g., the meter 200) to the sample so that a physical characteristic ofthe sample is determined from an output of the alternating signal. Thephysical characteristic being detected may be one or more of viscosity,hematocrit or density. The directing step may include driving first andsecond alternating signal at different respective frequencies in which afirst frequency is lower than the second frequency. Preferably, thefirst frequency is at least one order of magnitude lower than the secondfrequency. As an example, the first frequency may be any frequency inthe range of about 10 kHz to about 100 kHz and the second frequency maybe from about 250 kHz to about 1 MHz or more. As used herein, the phrase“alternating signal” or “oscillating signal” can have some portions ofthe signal alternating in polarity or all alternating current signal oran alternating current with a direct current offset or even amulti-directional signal combined with a direct-current signal.

Further refinements of Table 1 based on additional investigations of thetechnique allowed applicants to devise Table 2, shown below.

TABLE 2 Specified Sampling Time to Estimated G and Measured or EstimatedPhysical Characteristic Measured or Estimated Estimated PhysicalCharacteristic (e.g., HCT [%]) G [mg/dL] 24 27 30 33 36 39 42 45 48 5154 57 60 25 4.6 4.6 4.5 4.4 4.4 4.4 4.3 4.3 4.3 4.2 4.1 4.1 4.1 50 5 4.94.8 4.7 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4 4 75 5.3 5.3 5.2 5 4.9 4.8 4.7 4.54.4 4.3 4.1 4 3.8 100 5.8 5.6 5.4 5.3 5.1 5 4.8 4.6 4.4 4.3 4.1 3.9 3.7125 6.1 5.9 5.7 5.5 5.3 5.1 4.9 4.7 4.5 4.3 4.1 3.8 3.6 150 6.4 6.2 5.95.7 5.5 5.3 5 4.8 4.6 4.3 4 3.8 3.5 175 6.6 6.4 6.2 5.9 5.6 5.4 5.2 4.94.6 4.3 4 3.7 3.4 200 6.8 6.6 6.4 6.1 5.8 5.5 5.2 4.9 4.6 4.3 4 3.7 3.4225 7.1 6.8 6.5 6.2 5.9 5.6 5.3 5 4.7 4.3 4 3.6 3.2 250 7.3 7 6.7 6.4 65.7 5.3 5 4.7 4.3 4 3.6 3.2 275 7.4 7.1 6.8 6.4 6.1 5.8 5.4 5 4.7 4.3 43.5 3.2 300 7.5 7.1 6.8 6.5 6.2 5.8 5.5 5.1 4.7 4.3 4 3.5 3.1 w325 7.67.3 6.9 6.5 6.2 5.8 5.5 5.1 4.7 4.3 3.9 3.5 3.1 350 7.6 7.3 7 6.6 6.25.8 5.5 5.1 4.7 4.3 3.9 3.5 3.1 375 7.7 7.3 7 6.6 6.2 5.8 5.5 5.1 4.74.3 3.9 3.5 3.1 400 7.7 7.3 6.9 6.5 6.2 5.8 5.4 5 4.7 4.3 3.9 3.5 3.1425 7.6 7.3 6.9 6.5 6.2 5.8 5.4 5 4.6 4.3 3.8 3.5 3.1 450 7.6 7.2 6.86.4 6.1 5.7 5.3 5 4.6 4.3 3.8 3.5 3.1 475 7.4 7.1 6.7 6.4 6 5.6 5.3 4.94.6 4.2 3.8 3.5 3.1 500 7.3 7 6.6 6.2 5.9 5.5 5.2 4.9 4.5 4.1 3.8 3.53.2 525 7.1 6.8 6.5 6.1 5.8 5.5 5.1 4.8 4.4 4.1 3.8 3.5 3.2 550 7 6.76.3 5.9 5.6 5.3 5 4.7 4.4 4.1 3.8 3.5 3.2 575 6.8 6.4 6.1 5.8 5.5 5.24.9 4.6 4.3 4.1 3.8 3.5 3.4 600 6.5 6.2 5.9 5.6 5.3 5 4.7 4.5 4.3 4 3.83.6 3.4

As in Table 1, a measured or estimated physical characteristic is usedin Table 2 along with an estimated analyte concentration to derive atime S at which the sample is to be measured. For example, if themeasured charactertistic is about 30% and the estimated glucose (e.g.,by sampling at about 2.5 to 3 seconds) is about 350, the time at whichthe microcontroller should sample the fluid is about 7 seconds. Inanother example, where the estimated glucose is about 300 mg/dL and themeasured or estimated physical characteristic is 60%, the specifiedsampling time would be about 3.1 seconds.

For the embodiments utilized with Table 2, the estimated glucoseconcentration is provided with an equation:

$\begin{matrix}{G_{est} = \frac{\left( {I_{E} - x_{2}} \right)}{x_{1}}} & {{Eq}.\mspace{14mu} 6}\end{matrix}$

Where:

-   -   G_(est) represents the estimated glucose concentration;    -   I_(E) is the signal measured at about 2.5 seconds;    -   x₁ is the slope (e.g., x₁=1.3e01); and    -   x₂ is the intercept (e.g., x₂=6.9e02).

From the estimated glucose, the glucose concentration can be determinedfrom:

$\begin{matrix}{G_{o} = \frac{\left( {I_{s} - x_{4}} \right)}{x_{3}}} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

Where:

-   -   G_(o) represents the glucose concentration;    -   I_(s) is the signal measured at a specified sampling time S from        Table 2;    -   x₃ is the slope (e.g., x₃=9.6); and    -   x₄ is the intercept (e.g., x₄=4.8e02).

Although applicant's technique may specify only one sampling time point,the method may include sampling as many time points as required, suchas, for example, sampling the signal output continuously (e.g., atspecified sampling time such as, every 1 milliseconds to 100milliseconds) from the start of the test sequence until at least about10 seconds after the start and the results stored for processing nearthe end of the test sequence. In this variation, the sampled signaloutput at the specified sampling time (which may be different from thepredetermined sampling time point) is the value used to calculate theanalyte concentration.

It is noted that in the preferred embodiments, the measurement of asignal output for the value that is somewhat proportional to analyte(e.g., glucose) concentration is performed prior to the estimation ofthe hematocrit. Alternatively, the hematocrit level can be estimatedprior to the measurement of the preliminary glucose concentration. Ineither case, the estimated glucose measurement G_(E) is obtained byEquation 3.3 with I_(E) sampled at about one of 2.5 seconds or 5seconds, as in FIG. 7, the physical characteristic (e.g., Hct) isobtained by Equation 4 and the glucose measurement G is obtained byusing the measured signal output I_(D) at the designated sampling timepoint(s) (e.g., the measured signal output I_(D) being sampled at 3.5seconds or 6.5 seconds) for the signal transient 1000.

Other techniques for determining the analyte concentration or value areshown and described in PCT/GB2012/053276 (Attorney Docket No. DDI5220WOPCT) filed on Dec. 28, 2012, PCT/GB2012/053279 (Attorney DocketNo. DDI5246WOPCT) filed on Dec. 28, 2012; PCT/GB2012/053277 (AttorneyDocket No. DDI5228WOPCT) filed on Dec. 28, 2012, all of the applicationsare hereby incorporated by reference as if fully set forth herein with acopy attached to the appendix of this application.

Under actual operating conditions, the biosensor 100 may be used in anenvironment with ambient temperature varying widely from the testtemperature of about 22 degrees Celsius. In such cases, theelectrochemical reaction is less efficient at low temperatures causing awide bias to the actual measurement. Consequently, there is a need toensure that the analyte results are insensitive to the effects of theenvironmental temperature.

Referring to step 618 of FIG. 6, the system measures the temperatureproximate the biosensor 100 with a suitable temperature sensor, such as,for example, a thermistor built into the circuit board of the meter 200.Once temperature has been measured at step 618, the system utilizes anadditive temperature compensation term (which may in units of measures(e.g., mg/dL) or as a percentage) based on (1) a measured temperaturedifferent than 23 degrees Celsius and (2) as a function of differentmagnitudes of the measured analyte concentration to modify theuncompensated analyte value G₀ at step 620 and annunciate the modifiedor compensated final analyte value G_(F) at step 622.

In one embodiment, the system may utilize a plurality of temperaturecompensation terms for step 620 from FIG. 9. The compensation terms areused to adjust or correct the uncompensated value by applying thecompensation term to the uncompensated analyte value. The effect thiscompensation has on the uncompensated value is shown in FIG. 9 as afunction of bias to reference value. As a consequence, for uncompensatedanalyte values below a predetermined threshold (e.g., 100 mg/dL ofglucose), the system may be seen as adding the correction orcompensation term directly whereas, if the uncompensated value is at thethreshold or greater, the compensation factor would be an additive as apercentage of the uncompensated value. As an example of the first casewhere the uncompensated value is below the threshold of 100 mg/dL, theuncompensated analyte value was determined to be about 25 mg/dL and theambient temperature was 5 degrees Celsius, the compensation line CL1would be utilized to determine the compensation term of about 3 mg/dLthat would be added directly to the uncompensated value of 25 mg/dL togive a final compensated value of 28 mg/dL. In an example for the secondcase where the uncompensated value is at or above a predeterminedthreshold (e.g., 100 mg/dL of glucose), such as 350 mg/dL with measuredambient temperature of 10 degrees Celsius, the system would utilizecompensation line CL5 to add to the uncompensated value of 350 mg/dL acompensation term of 20% of the uncompensated value (20%*350=70 mg/dL)which would be added (to 350 mg/dL) to give the final value of 420mg/dL.

Referring back to FIG. 9, if the analyte (e.g., glucose) is about 25mg/dL, the temperature compensation term for temperature can be derivedgenerally from compensation line CL1; at about 75 mg/dL, the temperaturecompensation term generally follows compensation line CL2; at about 150mg/dL, the temperature compensation term generally follows compensationline CL3; at about 250 mg/dL then the temperature compensation termapplied to the uncompensated analyte value generally follows line CL4;and at about 350 mg/dL, the temperature compensation term applied to theuncompensated analyte value generally follows line CL5. In the eventthat the uncompensated analyte measurement is between any twocompensation lines, an interpolation can be made. To summarize FIG. 9,the temperature compensation lines or compensation terms for theuncompensated analyte values must conform to the following relationshipimplicitly defined in FIG. 9, in which:

-   -   (a) the temperature compensation term increases for increasing        uncompensated analyte values (which can be seen in FIG. 9 in        which the lines CL1-CL5 increases for increasing analyte values        (25, 75, 150, 250 and 350 mg/dL)); and    -   (b) the temperature compensation term is inversely related to        the ambient temperature proximate the biosensor from about 5        degrees Celsius to about 22 degrees Celsius; and    -   (c) the temperature compensation term is about zero for the        ambient temperature proximate the biosensor from about 22        degrees Celsius to about 45 degrees Celsius.

For a more precise compensation of the temperature as compared to therelationship in FIG. 9, the following equation (Eq. 8) can be utilized:

$\begin{matrix}{G_{F} = \frac{G_{0}}{1 + \frac{\begin{matrix}{{x_{1}\left( {{Temp} - {Temp}_{0}} \right)}^{3} + {x_{2}\left( {{Temp} - {Temp}_{0}} \right)}^{2} +} \\{x_{3}\left( {{Temp} - {Temp}_{0}} \right)}\end{matrix}}{{x_{4}\left( {\log \left( G_{0} \right)} \right)}^{3} + {x_{5}\left( {\log \left( G_{0} \right)} \right)}^{2} + {x_{6}\left( {\log \left( G_{0} \right)} \right)} + 1}}} & {{Eq}.\; 8}\end{matrix}$

Where:

-   -   G_(F) is the final glucose result;    -   G₀ is the uncompensated analyte value G glucose result (must be        ≧1);    -   Temp is the temperature measured by the meter (in ° C.);    -   Temp₀=22° C. (or a nominal temperature); and    -   x₁=4.69e-4, x₂=−2.19e-2, x₃=2.80e-1, x₄=2.99e0, x₅=−3.89e1, and        x₆=1.32e2.

Due to the nature of Equation 8, the uncompensated analyte measurementG₀ has to be set to 1 if it is less than 1 otherwise Equation 8 losesall meaning as the fitting function (governed by the log term foruncompensated analyte value below 1) diverges dramatically from expectedmeasurements. Equation 8 was utilized for 24 batches of the biosensor100. Results are summarized in graphical form in FIGS. 10 and 11A-11E.FIG. 10 presents the individual bias values for the same data. FIGS. 11Athrough 11E describe the entire data set.

As can be seen in FIG. 10, the majority of the analyte values, ascompared to reference analyte values, are within the bias of 10 mg/dLfor analyte measurements less than 100 mg/dL of the analyte (e.g.,glucose) and ±10% for analyte measurement at 100 mg/dL or greater. Curvefitting of the compensated measurements (line CT) shows that themeasurements are within these two bias boundaries.

As can be seen in each of FIGS. 11A-11E the average bias as compared tonominal temperature “T” for all batches with varying magnitudes (e.g.,40 mg/dL, 65 mg/dL, 120 mg/dL, 350 mg/dL) with respect to variousenvironmental temperatures (e.g., 6 degrees C., 12 degrees C., 22degrees C., 35 degrees C., and 44 degrees C.) indicates that the batchesare well within the bias boundaries of ±10 mg/dL for measurements below100 mg/dL (FIGS. 11A and 11B) and within the bias boundaries of ±10% formeasurements at 100 mg/dL or above (FIGS. 11C-11E).

To summarize the data provided herein, applicant's invention has allowedapplicant to obtain the technical contribution of enabling approximately97% of the biosensors to fall within ±15 mg/dL for measurements below100 mg/dL and ±15% for measurements at 100 mg/dL or greater. Anadditional technical contribution is provided by this invention in thatthe average bias to nominal bias is within ±10 mg/dL for measurementsbelow 100 mg/dL and ±10% for measurements at 100 mg/dL or greater. Bothof these technical contributions (enabled by applicant's invention) wereheretofore not available with applicant's current system (i.e.,One-Touch Ultra blood glucose measurement system).

Where the system has sufficient computing power, Equation 9 can beutilized in place of Equation 8. Specifically, the form of Equation 9is:

$\begin{matrix}{G_{F} = \frac{G_{0}}{1 + \frac{\begin{matrix}{{x_{1}\left( {{Temp} - {Temp}_{0}} \right)}^{3} + {x_{2}\left( {{Temp} - {Temp}_{0}} \right)}^{2} +} \\{x_{3}\left( {{Temp} - {Temp}_{0}} \right)}\end{matrix}}{{x_{4}\left( {G_{0} - G_{nom}} \right)}^{3} + {x_{5}\left( {G_{0} - G_{nom}} \right)}^{2} + {x_{6}\left( {G_{0} - G_{nom}} \right)} + x_{7}}}} & {{Eq}.\; 9}\end{matrix}$

Where:

-   -   G_(F) is the final analyte value;    -   G₀ is the uncompensated analyte value;    -   G_(nom) is a nominal analyte value;    -   Temp is the temperature measured by the meter (in ° C.);    -   Temp₀ is about 22° C. (or a nominal temperature); and    -   x₁ is about 4.80e-5, x₂ is about −6.90e-3, x₃ is about 2.18e-1,        x₄ is about 9.18e-6, x₅ is about −5.02e-3, x₆ is about 1.18e0,        and x₇ is about 2.41e-2.

Although the techniques described herein have been directed todetermination of glucose and compensating for the effect ofenvironmental temperature, the techniques can also applied to otheranalytes (with appropriate modifications by those skilled in the art)that are affected by physical characteristic(s) of the fluid sample inwhich the analyte(s) is disposed in the fluid sample. For example, thephysical characteristic (e.g., hematocrit, viscosity or density and thelike) of a physiological fluid sample could be accounted for indetermination of ketone or cholesterol in the fluid sample, which may bephysiological fluid, calibration, or control fluid. Other biosensorconfigurations can also be utilized. For example, the biosensors shownand described in the following US patents can be utilized with thevarious embodiments described herein: U.S. Pat. Nos. 6,179,979;6,193,873; 6,284,125; 6,413,410; 6,475,372; 6,716,577; 6,749,887;6,863,801; 6,860,421; 7,045,046; 7,291,256; 7,498,132, all of which areincorporated by reference in their entireties herein.

As is known, the detection of the physical characteristic does not haveto be done by alternating signals but can be done with other techniques.For example, a suitable sensor can be utilized (e.g., US PatentApplication Publication No. 20100005865 or EP1804048 B1) to determinethe viscosity or other physical characteristics. Alternatively, theviscosity can be determined and used to derive for hematocrits based onthe known relationship between hematocrits and viscosity as described in“Blood Rheology and Hemodynamics” by Oguz K. Baskurt, M.D., Ph.D., 1 andHerbert J. Meiselman, Sc.D., Seminars in Thrombosis and Hemostasis,volume 29, number 5, 2003.

As described earlier, the microcontroller or an equivalentmicroprocessor (and associated components that allow the microcontrollerto function for its intended purpose in the intended environment suchas, for example, the processor 300 in FIG. 2B) can be utilized withcomputer codes or software instructions to carry out the methods andtechniques described herein. Applicants note that the exemplarymicrocontroller 300 (along with suitable components for functionaloperation of the processor 300) in FIG. 2B is embedded with firmware orloaded with computer software representative of the logic diagrams inFIG. 6 and the microcontroller 300, along with associated connector 220and interface 306 and equivalents thereof, are the means for: (a)determining a specified sampling time based on a sensed or estimatedphysical characteristic, the specified sampling time being at least onetime point or interval referenced from a start of a test sequence upondeposition of a sample on the test strip and (b) determining an analyteconcentration based on the specified sampling time. Alternatively, themeans for determining may include means for applying a first signal tothe plurality of electrodes so that a batch slope defined by a physicalcharacteristic of a fluid sample is derived and for applying a secondsignal to the plurality of electrodes so that an analyte concentrationis determined based on the derived batch slope and the specifiedsampling time. Furthermore, the means for determining may include meansfor estimating an analyte concentration based on a predeterminedsampling time point from the start of the test sequence and forselecting a specified sampling time from a matrix of estimated analyteconcentration and sensed or estimated physical characteristic. Yetfurther, the means for determining may include means for selecting abatch slope based on the sensed or estimated physical characteristic andfor ascertaining the specified sampling time from the batch slope.

Moreover, while the invention has been described in terms of particularvariations and illustrative Figures, those of ordinary skill in the artwill recognize that the invention is not limited to the variations orFigures described. In addition, where methods and steps described aboveindicate certain events occurring in certain order, it is intended thatcertain steps do not have to be performed in the order described but inany order as long as the steps allow the embodiments to function fortheir intended purposes. Therefore, to the extent there are variationsof the invention, which are within the spirit of the disclosure orequivalent to the inventions found in the claims, it is the intent thatthis patent will cover those variations as well.

1. A method of adjusting for the effect of temperature upon a biosensorhaving a plurality of electrodes with at least two electrodes providedwith enzymes thereon, the method comprising the steps of: applying asignal to the at least two electrodes; initiating an electrochemicalreaction between the at least two electrodes and an analyte in a fluidsample to cause a transformation of the analyte into a byproduct;measuring a signal output from the at least two electrodes during theelectrochemical reaction; measuring a temperature proximate thebiosensor; calculating an analyte value representative of a quantity ofanalyte in the fluid sample from the signal output; adjusting theanalyte value to a final analyte value by a temperature compensationterm defined by a relationship where: (a) the temperature compensationterm increases for increasing analyte values; and (b) the temperaturecompensation term is inversely related to the biosensor temperature in arange of about 5 degrees Celsius to about 22 degrees Celsius; (c) thetemperature compensation term is about zero for the ambient temperatureproximate the biosensor from about 22 degrees Celsius to about 45degrees Celsius; and annunciating the final value representative of thequantity of analyte in the fluid sample.